DE 41 37 143 A1 has disclosed a multi-speed synchronized countershaft transmission where the gear positions of two gears are respectively coordinated with one of several shifting sets. Said shifting sets, as a rule, comprise sliding sleeves axially displaceably but non-rotatably situated upon a transmission shaft and which during a shifting operation, interacting with synchronizer rings adjacent to said sliding sleeves, decelerate idler gear wheels and can non-rotatably connect them with said transmission shaft.
In this known transmission, the two gears (first gear and third gear or second gear and fourth gear), coordinated with a shifting set, are two non-consecutive transmission gears. Said transmission construction has the advantage that a transmission shifting system is hereby created with which an overlapping shift actuation and therewith reduced shifting times are made possible. But it is a disadvantage that such a transmission cannot be shifted via a shifting device having an H-gate, since with one, such can usually be shifted in the same gate only two transmission gears which are immediately consecutive.
To overcome said problem, the pre-published DE 102 53 259.1 has one universally designable dual-clutch transmission which is essentially comprised of one starting unit, one core transmission and one output unit. The starting unit comprises a single clutch, one dual clutch, or one torque converter and the output unit contains transmission parts for a front-transverse drive, for a front-longitudinal drive, for a rear-longitudinal drive, or for an all-wheel drive of a vehicle. The core transmission is designed as a countershaft transmission having available at least one input shaft, one countershaft and one transmission output which is not coaxially oriented to at least one transmission output shaft.
The gear sequence in said transmission is such that beginning from the starting element (clutch) next to the fourth gear, the sixth gear, the second gear, the reverse gear, the seventh, the fifth, the third and the first gears follow. The fixed gears of the fourth, sixth, second and reverse gears are here non-rotatably fastened on a hollow shaft connected with the output side of one of the two clutches of a dual clutch, while the fixed gears of the seventh, the fifth, the third and the first gears are fastened on a second transmission input shaft coaxially supported in said hollow shaft and connected with the output side of the second clutch of the dual clutch.
DE 198 21 164 A1 has finally disclosed a six-gear dual-clutch transmission in which two fixed gears are situated upon a first transmission input shaft designed as hollow shaft. While the first fixed gear is meshed with one idler gear for the reverse gear and one second idler gear for the second gear, the second fixed gear meshed with one idler gear for the sixth gear, the same as with one idler gear for the fourth gear. Besides, in this transmission said idler gears for the reverse gear and the sixth gear are supported on a first countershaft while the idler gears for the second gear and the fourth gear are situated upon a second countershaft. This dual-clutch transmission is made comparatively short so that it can be used for front-transverse installation in vehicles. But a disadvantage is its comparatively large diameter which is determined by a total of six transmission shafts paraxial to each other of which the output shaft for the forward gears of the transmission is not shown.
With this background, the problem to be solved by the invention is to introduce a countershaft transmission, which due to its constructional features has a smaller diameter than the transmission according to DE 198 21 164 A1, is made comparatively short and can be designed as manually operable dual-clutch transmission or as manual selector transmission having only one starting and gear clutch.